Method of compacting, finishing, and curing concrete pavements



Patented May 26, 1931 UN'ETEETJD STATES PATEN QFFICIE PERCY A. HIPZPLE,OF ATLANTA, G ORGIA No Drawing.

,which consists in filling up the minute cavities or superficial poresof the pavement by means of the action of a fine spray of liquiddirected against the surface thereof. The material with which thecavities or superficial pores are thus filled may be the fine skim ofpure wet cement which normally accumulates on the surface of newly laidconcrete, or it ing of concrete pavements and involves the forcedremoval of entrapped air and the displacement of excess water from theconcrete mass by the injection of solid matter into the interior of themass.

The purpose of this invention is to provide: a means which willeffectively eliminate the surplus water, that is now left in concretepavement slabs, after various commercial machines, now in use forcompacting and finishing concrete pavement, have become ineffective; ameans whereby the water content of the fresh pavement slab is reduceduntil only moisture remains in the amount that is ideal for effectiveand uniform cementing action; a means whereby the entire body of thepavement is more thoroughly compacted and solidified; a means wherebyall pores both superficial and internal are thoroughly filled withdurable solid particles of materials of elemental similarity to theconcrete aggregate; a means whereby the pavement surface is so compactedand solidi lied that it will resist the evaporation of moisture, thatremains in the fresh finished slab for the purpose of hydration of thecement therein, thereby increasing and extending the efiective time ofcuring; a means whereby the pavement surface is so compacted andsolidified that the surface is effectively sealed against entry ofoutside moisture during the Application filed August 26, 1929. SerialNo. 388,636.

entire life of the pavement thus eliminating the subsequent damagecaused by expansion stresses and by freezing and thawing action that areset up within the pavement by the entry of moisture or water after thepavement is cured; and-a means whereby the mortar of the pavementsurface is so effectively compacted and solidified that it will betterre- Sist the abrasion and wear and tear of traflic.

t has been a well known fact for years that in mixing and placingconcrete for pavement slabs, it has been necessary to use a greateramount of water, in the process of mixing the concrete than the idealamount which should be present in the completed,

fresh pavement slab for the purpose of hydrating the cement therein, andin all commercial processes, of my knowledge, for compacting concretepavement, the compacting is done by the application of various tools tothe surface of the plastic concrete slab. All of these tools deliverpressure to the surface by various means; some having a tamping action,some, pressing and troweling and some vibrating and pressing.

Any of these commercial means above described cease to affect theconcrete mass, as soon as the larger aggregate particles in the concretemake firm contact with one another and form stress columns or archesfrom the top to the bottom of the mass. During the period of theseoperations in which the stress columns and arches are formed,the'finishing or compacting equipment exerts a direct influence on theentire mass of concrete and in t llS operation quite a bit of thesurplus'water and surplus mortar is displaced to the surface of theslab. I

As soon as thestress columns and arches form in the mass the existingmachines for compacting and finishing concrete slabs are renderedineffective in the further elimination of surplus Water and entrappedair that yet remains within the concrete mass. This is due to the factthat unpacked formations of mortar remain within the mass and theseformations are protected by the column and arching action of the coarseraggregate particles which column and arching action prevents furtheragitation of the unpacked mortar and prevents the forced expulsion ofthe remaining surplus water by these means.

Agitation, effected by the compacting or troweling action of the presentcommercial machines having ceased, the retained water is slowly releasedby the settling of the finer particles in the concrete mass. These finerparticles come to rest one against the other and have a tendency to freethe water and force it toward the surface of the slab. In the presentexisting methods of operation the removal of this slowly draining water,from the pavement surface, necessitates several operations of beltingand reworking over periods of time; and these operations cannot removeall the free water that remains near the surface of the slab.

The settling together of these finer particles effects the same columnand arch action among these finer particles as has previously occurredamong the larger particles of coarser aggregate, and in consequence,when the pavement is considered finished by the now existing methods theinterior of the concrete slab yet is honey combed with voids, each ofwhich voids is a receptacle for a globuleof water and this conditionespecially exists in the upper portion of the new pavement slab.

The belting operations, carried on for the purpose of removing the waterthat is accumulated on the surface, causes a quick rush of water whichadversely effects the natural action of the fine cement particles thatare present in or near the surface; and the globules of water that mayremain in the small interior voids act to disturb the fine cementparticles and retard their natural action.

I will herewith show that the finely pulverized impalpable' particles ofcement, which particles 1 will call cement flour, really prove to be theactive constituent of the cement; the coarser grains of cement beingpractically inert filler and also being vehicles for distribution of thecement flour throughout the mass. At the instant of contact withmoisture this cement fiour immediately attaches itself to the coarserparticles of cementor to the surface of any sand or stone with which itmay make contact. The interior of these coarser particles of cement andthe interior of the concrete aggregates, being dry, they absorb moistureand in the process of this absorption the moistened cement flour isdrawn into the capillaries of the coarser and more rugged materials.This establishes the relationship which later effects the cement bondthroughout the entire mass.

At the moment of complete saturation this cement flour forms ajelly-like substance which readily attaches itself to the surface of thecoarser particles of cement but this ellylike substance is found to berepellant to the presence of additional moisture or free water an'daslong as free surplus water is present in the concrete mass the cementflour remains inactive and is removed from the surface of the coarsermaterials by the film of water which inserts itself between. Hence it isseen that after a pavement is finished by the existing methods, thesurplus water that yet remains within the slab retards the naturalcementing action of the cement flour and holds it in suspension untilthe said surplus water has passed from the slab either by drainage orevaporation. The water content of the slab must, therefore, be reducedin volume until only moisture exists before complete and effectivecementing action is started, and after the cementing action is started 7it is desira le to maintain a uniformity of moisture within theslabuntil the cement is thoroughly set and the concrete is cured.

Present day standards require that 85% of the entire volume of cementused in con-} crete work, must be ground fine enough to pass a 200 meshsieve, the said sieve having 40,000 mesh openings per square inch. Inthe process of grinding the cement to this fineness quite a percentageof 300 to 400 mesh impalpable cement flour is produced and I haveauthority for the statement that an increase of fineness in the cementfrom 85% to 95% passing the 200 mesh sieve will increase the strength ofthe concrete 49% in all concrete wherein the cement used was ground to afineness where 95% would pass the 200 mesh sieve. The authoritativeconclusions drawn as to the cause of this extra developed strength beingthat the longer grinding of the cement, to produce the extra 10% of 200mesh particles, would thereby produce a greater amount" of impalpablecement flour;

which extra cement flour increases the strength of the cement. I haveauthority for the statement that cement will not set and harden if allthe particles smaller than the 200 mesh including the in'ipalpable flourare removed therefrom; the coarser particles being only inert fillerandvehicles of distribution for the vitally-necessary liner particles;therefore it is my purpose to correct existing conditions that tend toneutralize the proper action of any portion of the cement flour, in theoperation of compacting and finishing concrete pavements.

lVhereas the strength that may be developed in concrete slabs beingdependent upon the presence of this impalpable cement flour in theconcrete mass anv agency which prevents the even distribution of thisimpalp able cement throughout the concrete slab or which retards itscoalescence and colloidal action must necessarily-retard or prevent thedevelopment of the maximum strength in the concrete slab.

- Coalescence of the impalpable cement flour must take place and thesaidflour must form a colloidal or jelly-like paste free from disturbinginfluence of surplus Water before these particles will crystallize andstart their cementing action. This paste must evenly coat the surface,of the coarser grains of cement, and the entire surface of the sand andstone aggregate; and at the same time it must be freed from thedisturbing effect of any surplus water that may be present in the mass,before fully effective cementing action can be started and attained.

The facts above cited prove that moisture,

and not free water, is the effective agency of hydration of the cementin a concrete mass, and every commercial method, now in use, causesdamaging formations of free water in the upper portion of concretepavement slabs, without providing an efiecti-ve means for its completeremoval and expulsion from the slab.

I have discovered that, after the existing commercial machines forcompacting and finishing concrete pavements, have ceased to function,and during the period of natural settling of the liner particles in theconcrete mass, the presence of free water in the upper portion of theconcrete slab, causes the mortar of the upper portion to be extremelyplastic; and that itis practicable to shoot finely divided solids, intoand through the surface of this plastic mortar, with such force thatthey will penetrate deeply into the interior of the plastic mortar anddisplace the remaining water to the surface of the fresh laid pavementslab.

lVith the application of sufficient force to solid particles of theproper size, my herein described method becomes operative immediatelyafter the present commercial machines have ceased the operation of compar-ting, or pressing and troweling the surface, of the fresh concreteslab.

As soon as these machines cease operation, and while the surface iswater soaked and plastic, and without the lapse of time necessary forthe a pearance of the watersheen, as required in the process describedin my above mentioned Patent No. 1,175,088; the operation of my presentimproved method begins. The operation of the method is as follows: Ablast of sand, or a blast of finely d' ided solid particles of stone orother material that may become a lasting and elemental part of theconcrete slab, is directed at the surface of ti e fresh laid concreteslab; the actuating force being compressed air or other suitable means.7

In this operation the force of the compressed blast or other appliedpower is great enough to impel the solid particles through space, at andagainst the surface of the fresh concrete, with such momentum that theflying particles will penetrate, to the extreme depth of plasticbuoyancy, into the interior of the concrete slab; and should theirflight be arrested by inert particles in the plastic mass, will imparttheir momentum to the obstructing particles,

The multiplicity of impelled solid particles enter the fresh concretesurface and spend their forces in the manner of so many wedges beingdriven into the mass. As each individual particle comes to rest itdisplaces its volume, of Water, air or plastic mortar, which is forcedupward, and each succeeding particle in turn does likewise until all thesurplus water and entrapped air is driven out of the mass and replacedWith embedded solid particles to the' very top of the concrete slab. Inthis manner the elimination of the surplus water is followed from thedeep interior of the fresh concrete slab to the very surface, with apositive means to assure its expulsion. I

The impact of these impelled solids, and the friction engendered inentering and passing through the plastic and buoyant mortar, set upintermittent waves of hydrostatic pressure that cause the fine cement inthe concrete mass to better penetrate and fill the capillaries in thesurface of all the stone, sand and other aggregate in the concrete mass,as well as coating with cement, the

surface of the impelled solids; which solids come to rest in theinterior of the slab and remain as a part of the structure.

During the actual application of the blast of impelled solids theplastic mortar is penetrated with such high frequency that it fairlyboils upward under the intensity of this blast and as long as surplusWater remains in the mortar the mortar remains plastic and tends tolevel-itself off at the surface such as any fluid would do. lVhen enoughsand or other solid material has been shot into the concrete slab todisplace the volume of surplus water and entrapped air the surfaceimmediately becomes firm and of gritty texture, due to the fact that theprogress of the solidifying action was outward from the interior andthat the surface itself at the final period of the operation will resistimpact of the ini- -pelled solids,

The sizes of the impelled solids may be varied in accordance with thedepth of the slab, and the impact forces desired. The impelled solidsmay be of especially select and durable material to increase the Wearresistance of the pavement surface, since it is :manifest that with thecompletion of the pavement by this process, the surface will be loadedwith this material.

The'volume of the solids that may be impelled into and become a part ofthe concrete slab. is in direct proportion to the volume of water andentrapped air that may remain in the slab after the existing conrmercial methods, have ceased their effect.

This is a very small amount in relation to the entire mass of thepavement itself, but very important in that it displaces damaging waterand consequent voids and replaces same with solid durable materials.

In actual practice I have found that there is a uniformity ofdisplacement which is effected by my process over the entire slab of anygiven mixture of concrete and the completion of the operation of thisprocess over any fresh slab of concrete, leaves the surface as true anduniform of contour as it existed before the solids were applied; onlyadding a gritty texture at the very top.

To meet any argument, that may be raised, that the extra amount of solidmaterials, inipelled into the concrete slab by this process, mightreduce the cement ratio of the finished slab I- have found itpracticable to blast under low pressure, a coating mixture of purecement and water fluid over the fresh concrete surface immediatelybefore the application of the compacting blast of impelled solids. Thismixture can be varied, though one part cement to one and one half partswater seems to be the ideal consistency, and a calculated amount of thismixture of pure cement and water may be applied to the fresh concretesurface, to compensate for the subsequent reduction of the cement ratio.If desired, this cement fluid may be mixed with the solid particles andimpelled by the same force, at the same time.

The operation of my process efiects and accomplishes all the desirableresults above set forth in the description of the purpose of myinvention, far beyond the effective range of methods and equipment nowavailable for this purpose. 1

I find that the outward passing of the surplus water, which in presentcommercial methods of operation is uninterrupted in its tendency to washthe surface during the belting operation, is, in my method, changed indirection by the force of each impelled solid that enters the slab. Thischange of direction, at high frequency under the blast of impelledsolids, frees all the cement flour from the exuding water and causes thecement flour to remain in the pavement, in close contact with the solidstherein. I

I find that this process, effectively reduces the water content of thefresh concrete slab, until only moisture remains in the amount that isideal for effective and uniform cementing action; and I find that indisplacing the surplus water with solid materials, of elementalsimilarity to the concrete aggregate and in so doing, having alternatedthe flow of exuding water at high frequency and retained the cementflour for normal action in the surface of the slab; I have produced apavement surface, of such density, that the subsequent passage ofmoisture through the surface is greatly prevented.

This density of surface tends to retard the escape of the moistureremaining within the slab, for the purpose of hydration of the cementtherein, thus slowing down and prolonging the period of curing.

This density of surface also protects the which consists in initiallycompacting the freshly laid mass by external pressure upon the surfacethereof, and then internally compacting the mass and expelling air andexcess water from the interior of the mass by in jecting into the bodyof the mass particles of material of elemental similarity to theconcrete aggregate.

2. The process of indurating concrete which consists in initiallycompacting the freshly laid mass by external pressure upon the surfacethereof, and then internally compacting the mass and expelling air andexcess water from the interior of the mass by injecting thereinto, at ahigh velocity, particles of material of elemental similarity to theconcrete aggregate.

3. The process of indurating concrete which consists in partiallycompacting the solids in the mass thereby producing a top layer ofbuoyant water ladened plastic mortar, and then impelling finely dividedparticles of material of elemental similarity to the concrete aggregatethrough the layer of plastic mortar and into the main body of v the massby means of an air blast.

4. The process of indurating concrete which consists in partiallycompacting the solids in the mass thereby producing a top layer ofbuoyant water ladened plastic mortar, then impelling solid materialthrough said layer of plastic mortar into the interibr of the mass, andthen applying to-said mass a low pressure blast of pure cement mixedwith water to compensate for the reduction of cement ratio in theoriginal concrete mix effected by the injection of said solid particlesinto said mass.

5. The process of indurating concrete which consists in subjecting theplastic, freshly laid concrete mass to a blast of finely divided solidparticles which become an elemental part of the mass, the force of saidblast being sufficient to cause the solid particles to penetrate intothe interior of the concrete mass whereby their momentum will betransmitted to suspended particles originally incorporated in the masseffecting an internal compacting action upon the interior of the massand displacing therefrom entrapped air and surplus water. i

6. The process of indurating concrete which consists in subjecting theinterior of the freshly laid concrete mass to hydrostatic impulses ofhigh frequency and intensity, said impulses being engendered in thehydrated plastic mortar of the mass by the impact forces of finelydivided solids impelled against the surface of the fresh concrete withsufiicient momentum to cause their penetration into the interior of themass, whereby internal pressure created Within the mass causes the finecement particles originally incorporated in the concrete to betterpenetrate the capillaries therein and adhere to the surfaces of theaggregate in the concrete.

PERCY A. HIPPLE.

